The present invention relates to heparanase specific molecular probes their use in research and medical applications. More particularly, the present invention relates to the use of heparanase specific molecular probes, such as antisense oligonucleotide probes, antisense RNA probes, DNA probes and the like for detection and monitoring of malignancies, metastasis and other non-malignant conditions, efficiency of therapeutic treatments, targeted drug delivery and therapy.
Heparan sulfate proteoglycans (HSPGs): HSPGs are ubiquitous macromolecules associated with the cell surface and extracellular matrix (ECM) of a wide range of cells of vertebrate and invertebrate tissues (1-5). The basic HSPG structure consists of a protein core to which several linear heparan sulfate chains are covalently attached. The polysaccharide chains are typically composed of repeating hexuronic and D-glucosamine disaccharide units that are substituted to a varying extent with N- and O-linked sulfate moieties and N-linked acetyl groups (1-5). Studies on the involvement of ECM molecules in cell attachment, growth and differentiation revealed a central role of HSPGs in embryonic morphogenesis, angiogenesis, metastasis, neurite outgrowth and tissue repair (1-5). The heparan sulfate (HS) chains, unique in their ability to bind a multitude of proteins, ensure that a wide variety of effector molecules cling to the cell surface (4-6). HSPGs are also prominent components of blood vessels (3). In large vessels they are concentrated mostly in the intima and inner media, whereas in capillaries they are found mainly in the subendothelial basement membrane where they support proliferating and migrating endothelial cells and stabilize the structure of the capillary wall. The ability of HSPGs to interact with ECM macromolecules such as collagen, laminin and fibronectin, and with different attachment sites on plasma membranes suggests a key role for this proteoglycan in the self-assembly and insolubility of ECM components, as well as in cell adhesion and locomotion. Cleavage of HS may therefore result in disassembly of the subendothelial ECM and hence may play a decisive role in extravasation of blood-borne cells (7-9). HS catabolism is observed in inflammation, wound repair, diabetes, and cancer metastasis, suggesting that enzymes which degrade HS play important roles in pathologic processes.
Involvement of heparanase in tumor cell invasion and metastasis: Circulating tumor cells arrested in the capillary beds of different organs must invade the endothelial cell lining and degrade its underlying basement membrane (BM) in order to escape into the extravascular tissue(s) where they establish metastasis (10). Several cellular enzymes (e.g., collagenase IV, plasminogen activator, cathepsin B, elastase) are thought to be involved in degradation of the BM (10). Among these enzymes is an endo-β-D-glucuronidase (heparanase) that cleaves HS at specific intrachain sites (7, 9, 11-12). Expression of a HS degrading heparanase was found to correlate with the metastatic potential of mouse lymphoma (11), fibrosarcoma and melanoma (9) cells. Treatment of experimental animals with heparanase inhibitors (i.e. non-anticoagulant species of low MW heparin) markedly reduced (>90%) the incidence of lung metastases induced by B 16 melanoma, Lewis lung carcinoma and mammary adenocarcinoma cells (8, 9, 13).
Heparanase activity could not be detected in normal stromal fibroblasts, mesothelial, endothelial and smooth muscle cells derived from non cancerous biopsies and effusions (12). These observations indicate that heparanase expression may serve as a marker for tumor cells and in particular for those which are highly invasive or potentially invasive. If the same conclusion can be reached by immunostaining of tissue specimens, anti-heparanase antibodies may be applied for early detection and diagnosis of metastatic cell populations and micro-metastases.
Our studies on the control of tumor progression by its local environment, focus on the interaction of cells with the extracellular matrix (ECM) produced by cultured corneal and vascular endothelial cells (EC) (14, 15). This ECM closely resembles the subendothelium in vivo in its morphological appearance and molecular composition. It contains collagens (mostly type III and IV, with smaller amounts of types I and V), proteoglycans (mostly heparan sulfate- and dermatan sulfate-proteoglycans, with smaller amounts of chondroitin sulfate proteoglycans), laminin, fibronectin, entactin and elastin (13, 14). The ability of cells to degrade HS in the ECM was studied by allowing cells to interact with a metabolically sulfate labeled ECM, followed by gel filtration (Sepharose 6B) analysis of degradation products released into the culture medium (11). While intact HSPG are eluted next to the void volume of the column (Kav<0.2, Mr˜0.5×106), labeled degradation fragments of HS side chains are eluted more toward the Vt of the column (0.5<kav<0.8, Mr=5-7×103) (11).
Possible involvement of heparanase in tumor angiogenesis: Fibroblast growth factors are a family of structurally related polypeptides characterized by high affinity to heparin (16). They are highly mitogenic for vascular endothelial cells (EC) and are among the most potent inducers of neovascularization (16, 17). Basic fibroblast growth factor (bFGF) has been extracted from subendothelial ECM produced in vitro and from BM of the cornea, suggesting that ECM may serve as a reservoir for bFGF (18). Studies on the interaction of bFGF with ECM revealed that bFGF binds to HSPG in the ECM and can be released in an active form by HS degrading enzymes (19, 20). Heparanase activity expressed by platelets, mast cells, neutrophils, and lymphoma cells releases active bFGF from ECM and BM (20), suggesting that heparanase may not only function in cell migration and invasion, but may also elicit an indirect neovascular response (18). These results suggest that the ECM HSPGs provide a natural storage depot for bFGF and possibly other heparin-binding growth promoting factors. Displacement of bFGF from its storage within ECM may therefore provide a novel mechanism for induction of neovascularization in normal and pathological situations (6, 18).
Expression of heparanase by cells of the immune system: Heparanase activity correlates with the ability of activated cells of the immune system to leave the circulation and elicit both inflammatory and autoimmune responses. Interaction of platelets, granulocytes, T and B lymphocytes, macrophages and mast cells with the subendothelial ECM is associated with degradation of heparan sulfate (HS) by heparanase activity (7). The enzyme is released from intracellular compartments (e.g., lysosomes, specific granules) in response to various activation signals (e.g., thrombin, calcium ionophore, immune complexes, antigens, mitogens), suggesting its regulated involvement and presence in inflammatory sites and autoimmune lesions. Heparan sulfate degrading enzymes released by platelets and macrophages are likely to be present in atherosclerotic lesions (21). Hence, cDNA probes and anti-heparanase antibodies may be applied for detection and early diagnosis of these lesions.
Cloning and expression of the heparanase gene: The cloning and expression of the human heparanase gene are described in U.S. patent application Ser. No. 08/922,170, which is incorporated by reference as if fully set forth herein. A purified fraction of heparanase isolated from human hepatoma cells was subjected to tryptic digestion. Peptides were separated by high pressure liquid chromatography and micro sequenced. The sequence of one of the peptides was used to screen data bases for homology to the corresponding back translated DNA sequence. This procedure led to the identification of a clone containing an insert of 1020 base pairs (bp) which included an open reading frame of 963 by followed by 27 by of 3′ untranslated region and a Poly A tail. The new gene was designated hpa. Cloning of the missing 5′ end of hpa cDNA was performed by PCR amplification of DNA from placenta cDNA composite. The plasmid containing the entire heparanase cDNA was designated phpa. The joined cDNA fragment contained an open reading frame which encodes a polypeptide of 543 amino acids with a calculated molecular weight (MW) of 61,192 daltons. The ability of the hpa gene product to catalyze degradation of heparan sulfate (HS) in vitro was examined by expressing the entire open reading frame of hpa in High five and Sf21 insect cells, using the Baculovirus expression system. Extracts of infected cells were assayed for heparanase activity. For this purpose, cell lysates were incubated with sulfate labeled, ECM-derived HSPG (peak I), followed by gel filtration analysis (Sepharose 6B) of the reaction mixture. While the substrate alone consisted of high molecular weight (MW) material, incubation of the HSPG substrate with lysates of cells infected with hpa containing virus resulted in a complete conversion of the high MW substrate into low MW labeled heparan sulfate degradation fragments.
In subsequent experiments, the labeled HSPG substrate was incubated with the culture medium of infected High Five and Sf21 cells. Heparanase activity, reflected by the conversion of the high MW HSPG substrate into low MW HS degradation fragments, was found in the culture medium of cells infected with the pFhpa virus, but not the control pF1 virus. Altogether, these results indicate that the heparanase enzyme is expressed in an active form by cells infected with Baculovirus containing the newly identified human hpa gene. In other experiments, we have demonstrated that the heparanase enzyme expressed by cells infected with the pFhpa virus is capable of degrading HS complexed to other macromolecular constituents (e.g., fibronectin, laminin, collagen) present in a naturally produced intact ECM, in a manner similar to that reported for highly metastatic tumor cells or activated cells of the immune system.
Purification of the recombinant heparanase enzyme: The purification of the human heparanase gene are described in U.S. patent application Ser. No. 08/922,170, which is incorporated by reference as if fully set forth herein. Sf21 insect cells were infected with pFhpa virus and the culture medium was applied onto a heparin-Sepharose column. Fractions were eluted with a salt gradient (0.35-2 M NaCl) and tested for heparanase activity and protein profile (SDS/PAGE followed by silver staining). Heparanase activity correlated with the appearance of a protein band of about 63 kDa in fractions 19-24, consistent with the expected MW of the hpa gene product. Active fractions eluted from heparin-Sepharose were pooled, concentrated and applied onto a Superdex 75 FPLC gel filtration column. Aliquots of each fraction were tested for heparanase activity and protein profile. A correlation was found between the appearance of a major protein of about 63 kDa in fractions 4-7 and heparanase activity. This protein was not present in medium conditioned by control non-infected Sf21 cells and subjected to the same purification protocol.
Research on the involvement of heparanase/HS in tumor cell metastasis and angiogenesis has been handicapped by the lack of biological tools (i.e., molecular probes, antibodies) to explore a causative role of heparanase in disease. U.S. patent application Ser. No. 08/922,170 offers, for the first time, a good opportunity to elucidate the enzyme's involvement in tumor metastasis and angiogenesis and the related diagnostic applications.
On the basis of the examples described below, it appears that cDNA and RNA probes, PCR primers, and anti-heparanase antibodies (heparanase specific molecular probes) can be applied to detect the heparanase gene and protein and hence for early diagnosis of micrometastases, autoimmune lesions, renal failure and atherosclerotic lesions using biopsy specimens, plasma samples, and body fluids.
Specificity and advantages over other reported antibodies: A variety of blood, tumor cells and certain normal cells have been shown to produce significant amounts of heparanase activity. The purification to homogeneity and characterization of mammalian heparanases has been difficult, primarily due to the lack of a convenient assay. Most reports contain only partial description with conflicting information. Oosta, et al. (22) described the purification of a human platelet heparanase with an estimated molecular mass of 134 kDa expressing an endoglucuronidase activity. Hoogewert, et al. (23) reported the purification of a 30 kDa human platelet heparanase which was shown to be an endoglucosaminidase that cleave both heparin and heparan sulfate essentially to disaccharides. They claimed that the holoenzyme consists of four subunits, each closely related to the CXC chemokines CTAPIII, NAP-2 and β-thromboglobulin (23). Freeman and Parish (24) have purified to homogeneity a 50 kDa platelet heparanase exhibiting endoglucuronidase activity. Likewise heparanase enzyme purified from human placenta and from hepatoma cell line (U.S. Pat. No. 5,362,641) had a molecular mass of approximately 48 kDa. A similar molecular weight was determined by gel filtration analysis of partially purified heparanase enzymes isolated form human platelets, human neutrophils and mouse B16 melanoma cells (our unpublished data). In contrast, heparanase purified from B16 melanoma cells by Nakajima, et al. (9, 26) had a molecular weight of 96 kDa. The latter enzyme has been localized immunochemically to the cell surface and cytoplasm of human melanoma lesions using a polyclonal antiserum (26) and in tertiary granules in neutrophils using monoclonal antibodies (26a), both directed against a putative amino terminal sequence from purified B16F10 melanoma cell heparanase (26). However, the melanoma heparanase amino terminal sequence was found to be characteristic of a 94 kDa glucose-regulated protein (GRP94/endoplasmin) that functions as a molecular chaperone which lacks heparanase activity (27). This result and a recent study using anti-endoplasmin antibody (28) suggest that the endoplasmin-like 98 kDa protein found in purified melanoma heparanase preparations is a contaminant (27, 28). This calls into question the previous heparanase immunolocalization studies carried out using the B16 melanoma heparanase amino terminal peptide antiserum (26). Likewise, antiserum directed against the amino terminal sequence of CTAP III was applied to immunolocalize the heparanase enzyme in biopsy specimens of human prostate and breast carcinomas (29, 30). Again, the validity of the results is questionable, since the possibility that CTAP III is a contaminant of the platelet preparation was not excluded. First, attempts to express heparanase active CTAPIII/NAP2 protein were unsuccessful and the recombinant CTAPIII/NAP2 chemokines failed to exhibit heparanase activity. Second, western blot analysis of the platelet enzyme purified by Freeman and Parish (24) with antibodies against human β-thromboglobulin or platelet factor-4 demonstrated that these and related proteins (e.g., CTAP-III and NAP-2) were not present in the purified platelet heparanase preparations (24). Moreover, while heparanase activity can be detected in purified preparations of β-thromboglobulin, it is probably due to contamination with the “classical” platelet heparanase since it exhibited an endo-beta-D-glucuronidase activity rather than an endoglucosaminidase activity (23), as reported by Hoogewerf et al. (Pikas et al. manuscript submitted for publication).
Our studies on the immunolocalization of CTAPIII in human biopsy specimens revealed a preferential localization of CTAP-III in cells (i.e., vascular endothelia cells, keratinocytes) that failed to express heparanase activity and vice versa. Finally, none of the sequences published by Hoogewerf et al (platelet CTAP-III/NAP-2) (23) or Jin et al. (B16 melanoma) (26) nor sequences of the bacterial heparin/heparan sulfate degrading enzymes (hep I & III) (30a) were found in our recombinant human heparanase that was cloned and expressed on the basis of sequences derived from the purified human placenta and hepatoma heparanases.
Several years ago we prepared rabbit polyclonal antibodies directed against our partially purified preparation of human placenta heparanase. These antibodies, referred to in U.S. Pat. No. 5,362,641, were later found to be directed against plasminogen activator inhibitor type I (PAI-1) that was co-purified with the placental heparanase. These findings led to a modification of the original purification protocol to remove the PAI-1 contaminant.
Collectively, it is evident that so far no one had succeeded in eliciting anti-heparanase antibodies.
Unlike the above described information, both the polyclonal and monoclonal antibodies described hereinunder were raised, for the first time, against a purified, highly active, recombinant enzyme. As further shown below these antibodies specifically recognizes the heparanase enzyme in cell lysates and conditioned media and does not cross-react with β-thromboglobulin, NAP-2, PAI-1 or bacterial heparinases I and III. They do recognize the mouse B16-F10 heparanase, the human platelet heparanases, and the heparanase enzymes produced by several human tumor cell lines and Chinese hamster ovary (CHO) cells. By virtue of being produced against a purified recombinant enzyme and their specificity, these antibodies appear highly appropriate for diagnostic purposes such as immunohistochemistry of biopsy specimens and quantitative ELISA of body fluids (e.g., plasma, urine, pleural effusions, etc.). Similarly, as presented in the Examples section hereinunder, both the molecular probes for in situ determination of the tissue distribution of the hpa gene and the cDNA primers for detection of the hpa mRNA in normal and malignant cells of human origin (e.g., leukemia and lymphoma cells, melanoma cells) can be applied, for the first time, for diagnosis of early events in tumor progression, metastatic spread and response to treatment.